This invention relates to a process for production of hydrogen peroxide from hydrogen and oxygen with a gold-containing supported catalyst. Surprisingly, this catalyst system produces hydrogen peroxide in the liquid-phase reaction of hydrogen and oxygen.
Many different methods for the preparation of hydrogen peroxide have been developed. Commercially, the most common method of produce hydrogen peroxide is the xe2x80x9canthraquinonexe2x80x9d process. In this process, hydrogen and oxygen react to form hydrogen peroxide by the alternate oxidation and reduction of alkylated anthraquinones in organic solvents. A significant disadvantage of this process is that it is costly and produces a significant amount of by-products that must be removed from the process. On account of these problems, much research has been conducted with the goal of developing an alternative to the anthraquinone process.
One promising method involves the direct production of hydrogen peroxide by the reaction of hydrogen and oxygen in the presence of a catalyst. Various catalysts have been developed for the direct production of hydrogen peroxide. Typical catalysts include palladium-containing catalysts, although other metals such a gold can be added as additional components as an alloy or a mixture (see e.g. U.S. Pat. No. 5,320,821).
JP 07-241473 discloses a process whereby hydrogen peroxide is produced by the reaction of hydrogen and oxygen in an acidic aqueous solution in the presence of the catalyst comprising fine gold particles supported on hydrophobic carrier. The hydrophobic carrier includes silicalite, polyethylene, polypropylene, and polytetrafluoroethylene.
As with any chemical process, new catalysts are desired. We have discovered an effective, convenient catalyst for the direct production of hydrogen peroxide from hydrogen and oxygen.
The invention is a process to produce hydrogen peroxide that comprises reacting hydrogen and oxygen in an oxygenated solvent in the presence of a supported catalyst comprising gold and a support, wherein the support is a non-zeolitic inorganic oxide containing titanium or zirconium. It is surprisingly found that the catalyst produces hydrogen peroxide.
The process of the invention employs a supported catalyst comprising gold and a support. The support is non-zeolitic inorganic oxide that contains titanium or zirconium. The amount of titanium or zirconium present in the support is preferably in the range from about 0.1 to about 75 weight percent. Preferred supports include titania, zirconia, and amorphous titania-silica or zirconia-silica. These non-zeolitic supports are hydrophilic in nature.
Titania-silicas or zirconia-silicas comprise an inorganic oxygen compound of silicon in chemical combination with an inorganic oxygen compound of titanium or zirconium (e.g. an oxide or hydroxide of titanium or zirconium). The inorganic oxygen compound of titanium or zirconium is preferably combined with the oxygen compound of silicon in a high positive oxidation state, e.g., as tetravalent titanium or zirconium. The amount of titanium (zirconium) contained in the titania(zirconia)-silica support can be varied. Typically, the support contains at least 0.1% by weight of titanium or zirconium with amounts from about 0.2% by weight of about 50% by weight being preferred and amounts from about 0.2% to about 10% by weight being most preferred. Titania(zirconia)-silicas are well -known in the art and are described, for example, in U.S. Pat. Nos. 4,367,342 and 6,011,162.
The supported catalyst useful in the process of the invention also contains gold. The typical amount of gold present in the catalyst will be in the range of from about 0.01 to 20 weight percent, preferably 0.01 to 10 weight percent, and most preferably 0.01 to 5 weight percent. While various methods known to those skilled in the art may be used, preferably the gold may be supported by a deposition-precipitation method in which a gold compound is deposited and precipitated on the surface of the support by controlling the pH and temperature of the aqueous gold solution (as described in U.S. Pat. No. 5,623,090).
There are no particular restrictions regarding the choice of gold compound used in the preparation of the supported catalyst. For example, suitable compounds include gold halides (e.g., chlorides, bromides, iodides), cyanides, and sulfides. Chloroauric acid is particularly useful.
The supported catalyst may be used in the process of the invention as a powder or as a pellet or extrudate. If pelletized or extruded, the supported catalyst may additionally comprise a binder or the like and may be molded, spray dried, shaped or extruded into any desired form prior to use in epoxidation.
The process of the invention comprises contacting hydrogen and oxygen in an oxygenated solvent in the presence of the supported catalyst. The oxygenated solvent may be any chemical that is a liquid under reaction conditions that contains at least one oxygen atom in its chemical structure. Suitable oxygenated solvents include water and oxygen-containing hydrocarbons such as alcohols, ethers, esters, ketones, and the like. Preferred oxygenated solvents include lower aliphatic C1-C4 alcohols such as methanol, ethanol, isopropanol, and tert-butanol, or mixtures thereof, and water. Fluorinated alcohols can be used. It is also possible to use mixtures of the cited alcohols with water. Particularly preferred oxygenated solvents include water, methanol, and a mixture of methanol and water. For mixtures of methanol and water, the molar ratio of methanol:water is preferably within the range of from about 3 to about 6.
Oxygen and hydrogen are also required for the process of the invention. Although any sources of oxygen and hydrogen are suitable, molecular oxygen and molecular hydrogen are preferred. The molar ratio of hydrogen to oxygen can usually be varied in the range of H2:O2=1:10 to 5:1 and is especially favorable at 1:2 to 2:1.
In addition to oxygen and hydrogen, an inert gas carrier may be preferably used in the process. As the carrier gas, any desired inert gas can be used. Suitable inert gas carriers include noble gases such as helium, neon, and argon in addition to nitrogen, methane, and carbon dioxide. Nitrogen is the preferred inert carrier gas. Mixtures of the listed inert carrier gases can also be used.
For the liquid-phase process of the invention, the catalyst is preferably in the form of a suspension or fixed-bed. The process may be performed using a continuous flow, semi-batch or batch mode of operation. It is advantageous to work at a pressure of 1-100 bars. The reaction process according to the invention is carried out at a temperature effective to achieve the desired hydrogen peroxide formation, preferably at temperatures in the range of 0-100xc2x0 C., more preferably, 20-60xc2x0 C.
The following examples merely illustrate the invention. Those skilled in the art will recognize many variations that are within the spirit of the invention and scope of the claims.